Stress wears many faces. Sometimes it is loud: a racing heart before a tough conversation, sweaty palms in an interview. Other times it is quiet: a restless night, a short fuse, a mind that will not switch off. It can be set off by the world around you or by your internal state: light that is too bright at midnight, a meal that spikes blood sugar, the slow toll of pollution, noise, pain, or loss.
It is not always “in your head”. Stress is a full body response. Every organ system, from your heart to your gut to your immune cells, is primed to respond. In small doses, stress can be life saving: it sharpens focus and prepares you to take action. But when stress signals never switch off, they change how you sleep, heal, think, and even how quickly you age. Understanding what is happening in your body is the first step to taking control over reducing stress.
Types of stress (responses)
Stress is not uniform. The body responds differently depending on the situation, the intensity, and the duration of the challenge. It also depends on the individual and their coping strategies.
When a trigger signals the brain, it creates mental strain. This sets off a cascade of imbalances across hormonal, immune, and cellular functions. You may feel it as a racing heart or tense muscles, and less visible subtle shifts in your DNA repair processes.
- Acute stress: A short burst of stress in response to a clear, immediate challenge – swerving to avoid a crash or delivering an important presentation. These episodes mobilise energy, sharpen focus and, when followed by full recovery, can strengthen the body’s defences.
- Chronic stress: The ‘always on’ state. It may stem from ongoing caregiving, persistent work strain or unsafe living conditions. Without adequate recovery, chronic activation fuels inflammation, disrupts metabolism and accelerates biological ageing.
- Episodic acute stress: Frequent spikes of acute stress, common in chaotic schedules or high conflict environments. The body gears up repeatedly leading to cumulative wear and tear.
- Traumatic stress: Triggered by extreme events – assaults, disasters or combat. It can persist long after the event via memories, cues or flashbacks.
Each pattern leaves a distinct physiological footprint. Acute stress can build resilience. Chronic or repeated spikes without adequate recovery erode resilience and impair health.
Types of stressors (triggers that set stress in motion)
Stressors can be external: a looming deadline, an argument, a heatwave, or internal: an infection, chronic inflammation or hormonal imbalance. These stress inducing events challenge the body and trigger stress response.
- Environmental stressors: External pressures – noise, crowding, extreme temperatures, pollution and sudden environmental change – can activate the stress response. At the cellular level, exposures include ionising radiation, heavy metals and oxidative stress.
- Psychological stressors: Pressures arising from thoughts, emotions or relationships; from work deadlines and academic demands to social comparison and self imposed expectations, can activate and sustain the stress response. Humans can anticipate and recall threats even when none is physically present.
- Physiological stressors: Internal challenges such as infection, injury, surgery, chronic pain, blood sugar swings or hormonal imbalance trigger the stress response and prompt repair and immune activation; when persistent, they can drive inflammation and metabolic disruption.
You can’t always avoid stressors, the world is full of them. But you can change how your body reacts and how long it stays in “alert mode.” Two people can face the same stressor and walk away with entirely different outcomes, depending on their resilience, recovery habits, and overall health.
Over time, the sum of all the stressors you have faced shapes how your systems function. The more frequent and prolonged the activations without recovery, the greater the wear on your hormonal, immune and metabolic systems, and the faster biological ageing can progress.
Stress response pathways
Stress response is the body’s coordinated system for handling any challenge that threatens internal balance. It operates through tightly linked networks in the brain, endocrine, and immune system. The pathways that switch on – and for how long – determine whether the effects are protective or harmful.
Neural circuitry regulating stress
Every stress response begins in the brain, where incoming information is assessed and a decision to act is made.
Key brain regions
- Amygdala: Detects potential threats rapidly.
- Hippocampus: Provides contextual memory to shape the response.
- Prefrontal cortex: Regulates and balances the response via top-down control.
- Insula: Monitors internal body states for cues.
- Locus coeruleus: The brain’s primary source of noradrenaline, increasing alertness.
How it starts: The amygdala quickly flags potential threats; the hippocampus checks past experiences to judge risk; the prefrontal cortex weighs the evidence and modulates the reaction. If action is needed, the brain activates:
- sympatho-adreno-medullary (SAM) axis: the rapid, seconds-to-minutes response.
- hypothalamic-pituitary-adrenal (HPA) axis: the slower, minutes-to-hours response.
These systems evolved to handle short term, high priority demands.
Sympatho-adreno-medullary (SAM) axis
The SAM axis activates almost instantly in response to a potential threat.
How it starts: The brain detects a challenge, and the hypothalamus together with brainstem centres sends activation signals down the sympathetic nervous system. This simultaneously:
- releases noradrenaline directly from sympathetic nerves to target tissues;
- triggers the adrenal medulla to release adrenaline and noradrenaline into the bloodstream.
What happens in the body: Catecholamines bind to receptors in the heart, lungs, blood vessels and other organs, leading to:
- increasing heart rate and strengthening cardiac contractions
- accelerating breathing and widening airways
- redirecting blood flow towards skeletal muscle
- mobilising glucose and fats for rapid energy
- slow digestion
- dilating pupils and heightening attention.
The SAM response peaks within seconds to minutes and should settle once the challenge ends.
When it helps vs. when it harms
- Helps: Short bursts sharpen focus, reaction speed and safety in urgent situations.
- Harms: Repeated activation without recovery can keep blood pressure elevated, disrupt sleep, impair glycaemic control and entrench chronic stress patterns.
Hypothalamic–pituitary–adrenal (HPA) axis
The HPA axis takes longer to activate than SAM but sustains the stress response for minutes to hours.
How it starts: The hypothalamus releases corticotropin-releasing hormone (CRH), which signals the pituitary gland to release adrenocorticotropic hormone (ACTH). ACTH travels via the bloodstream to the adrenal cortex, prompting cortisol release.
What cortisol does:
- Energy supply: Raises blood glucose and reduces insulin sensitivity to keep fuel available.
- Cardiovascular support: Makes blood vessels more responsive to adrenaline and noradrenaline.
- Immune regulation: Temporarily dampens excessive inflammation but, when elevated chronically, weakens antiviral defences and promotes low grade inflammation.
- Cognition and mood: Heightens threat detection and focus, but prolonged elevation can narrow attention and raise anxiety.
- Trade offs: Suppresses reproductive signalling and slows some tissue growth and repair.
Builds over tens of minutes and can persist for hours. In a healthy pattern, activity tapers once the stressor passes, preserving the daily rhythm of high morning and low evening cortisol.
When it helps vs. when it harms
- Helps: Sustains performance, supports recovery and controls inflammation.
- Harms: Chronic activation without recovery contributes to abdominal fat gain, insulin resistance, high blood pressure, disrupted sleep, low mood and memory problems.
Link to immune system, inflammation and oxidative stress
The immune system and stress pathways are closely linked. When your body prepares for a challenge, it also prepares for the possibility of injury or infection.
Immunity and inflammation: The SAM axis releases adrenaline and noradrenaline, acting on receptors in immune cells, while the HPA axis releases cortisol to adjust inflammatory responses.
- Acute stress: Immune cells (neutrophils, monocytes, natural killer cells) move rapidly from storage into the blood, then to barrier sites such as skin and mucosa; inflammation rises temporarily to handle potential injury.
- Chronic stress: Prolonged hormone exposure can make immune cells less sensitive to cortisol’s anti-inflammatory effects (glucocorticoid resistance). Pro-inflammatory signals such as IL-6 and TNF-α remain active, antiviral defences weaken and healing slows.
Acute changes occur within minutes and resolve within hours. Chronic stress can shift immune function for weeks, months or longer.
Oxidative stress: Stress leaves measurable changes inside cells. One of the most important is oxidative stress – an imbalance between reactive oxygen species (ROS) and the body’s antioxidant defences. High oxidative stress accelerates tissue decline and raises the risk of cardiovascular disease, diabetes and neurodegenerative conditions.
Not all stress is harmful. In controlled doses, it can trigger adaptations that make the body stronger – a process known as hormesis. The opposite – toxic activation – occurs when stress is too frequent, too intense or does not fully resolve.
When can stress be good?
In the right dose, stress can strengthen the very systems it activates. This beneficial form is called eustress. It works by engaging stress pathways just enough to prompt adaptation, followed by full recovery.
What happens when in eustress
- Sharper focus and faster reaction speed
- Improved immune readiness and wound healing shortly after exposure
- Enhanced memory for important cues
- Activation of cellular repair systems, including antioxidant defences
Eustress is not about living without challenges; it is about having challenges within your capacity to meet. Without adequate recovery, even eustress can shift into toxic stress – eroding the same systems it once strengthened.
Manage stress with these lifestyle recommendations
Breaking chronic stress patterns does not require a complete overhaul. The goal is to create steady, repeatable signals that help the body return to balance:
- Build awareness: Make note of when you feel tense, drained, foggy or ‘wired’, and start recognising the obvious or subtle triggers that set those states in motion.
- Prioritise rest: Keep a regular sleep-wake rhythm, reduce evening screen light and take short breaks during the day to reset.
- Move regularly: Walk, stretch or do light strength work, and spend time in natural light to reinforce your circadian rhythm.
- Eat for stability: Choose balanced meals that steady blood sugar and support gut health with fibre rich and fermented foods.
- Use your breath: Slow, controlled breathing can quickly shift the body into ‘rest and repair’ mode.
- Reduce sensory load: Limit constant notifications and create no-screen windows in your day.
- Stay connected: Maintain relationships that offer genuine support and ease.
These habits do more than relieve stress in the moment. Practised consistently, they protect long-term resilience and help prevent the constant activation that fuels inflammation, metabolic strain and faster biological ageing.
We all get stressed. Stress does not come in ‘small’ or ‘big’ sizes, and its impact on your body is not always visible.
The goal is not to chase a life without stress. It is to understand what sets you off – what makes you tense, agitated, foggy or drained – and to pause long enough to notice it. Ask yourself: where is this feeling coming from? Naming it is often the first step to changing your response.
